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Connexins in the Heart: Regulation, Function and Involvement in Cardiac Disease. Int J Mol Sci 2021; 22:ijms22094413. [PMID: 33922534 PMCID: PMC8122935 DOI: 10.3390/ijms22094413] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 04/12/2021] [Accepted: 04/20/2021] [Indexed: 12/20/2022] Open
Abstract
Connexins are a family of transmembrane proteins that play a key role in cardiac physiology. Gap junctional channels put into contact the cytoplasms of connected cardiomyocytes, allowing the existence of electrical coupling. However, in addition to this fundamental role, connexins are also involved in cardiomyocyte death and survival. Thus, chemical coupling through gap junctions plays a key role in the spreading of injury between connected cells. Moreover, in addition to their involvement in cell-to-cell communication, mounting evidence indicates that connexins have additional gap junction-independent functions. Opening of unopposed hemichannels, located at the lateral surface of cardiomyocytes, may compromise cell homeostasis and may be involved in ischemia/reperfusion injury. In addition, connexins located at non-canonical cell structures, including mitochondria and the nucleus, have been demonstrated to be involved in cardioprotection and in regulation of cell growth and differentiation. In this review, we will provide, first, an overview on connexin biology, including their synthesis and degradation, their regulation and their interactions. Then, we will conduct an in-depth examination of the role of connexins in cardiac pathophysiology, including new findings regarding their involvement in myocardial ischemia/reperfusion injury, cardiac fibrosis, gene transcription or signaling regulation.
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Lara R, Adinolfi E, Harwood CA, Philpott M, Barden JA, Di Virgilio F, McNulty S. P2X7 in Cancer: From Molecular Mechanisms to Therapeutics. Front Pharmacol 2020; 11:793. [PMID: 32581786 PMCID: PMC7287489 DOI: 10.3389/fphar.2020.00793] [Citation(s) in RCA: 93] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Accepted: 05/13/2020] [Indexed: 12/18/2022] Open
Abstract
P2X7 is a transmembrane receptor expressed in multiple cell types including neurons, dendritic cells, macrophages, monocytes, B and T cells where it can drive a wide range of physiological responses from pain transduction to immune response. Upon activation by its main ligand, extracellular ATP, P2X7 can form a nonselective channel for cations to enter the cell. Prolonged activation of P2X7, via high levels of extracellular ATP over an extended time period can lead to the formation of a macropore, leading to depolarization of the plasma membrane and ultimately to cell death. Thus, dependent on its activation state, P2X7 can either drive cell survival and proliferation, or induce cell death. In cancer, P2X7 has been shown to have a broad range of functions, including playing key roles in the development and spread of tumor cells. It is therefore unsurprising that P2X7 has been reported to be upregulated in several malignancies. Critically, ATP is present at high extracellular concentrations in the tumor microenvironment (TME) compared to levels observed in normal tissues. These high levels of ATP should present a survival challenge for cancer cells, potentially leading to constitutive receptor activation, prolonged macropore formation and ultimately to cell death. Therefore, to deliver the proven advantages for P2X7 in driving tumor survival and metastatic potential, the P2X7 macropore must be tightly controlled while retaining other functions. Studies have shown that commonly expressed P2X7 splice variants, distinct SNPs and post-translational receptor modifications can impair the capacity of P2X7 to open the macropore. These receptor modifications and potentially others may ultimately protect cancer cells from the negative consequences associated with constitutive activation of P2X7. Significantly, the effects of both P2X7 agonists and antagonists in preclinical tumor models of cancer demonstrate the potential for agents modifying P2X7 function, to provide innovative cancer therapies. This review summarizes recent advances in understanding of the structure and functions of P2X7 and how these impact P2X7 roles in cancer progression. We also review potential therapeutic approaches directed against P2X7.
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Affiliation(s)
- Romain Lara
- Biosceptre (UK) Limited, Cambridge, United Kingdom
| | - Elena Adinolfi
- Department of Medical Sciences, University of Ferrara, Ferrara, Italy
| | - Catherine A Harwood
- Centre for Cell Biology and Cutaneous Research, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom
| | - Mike Philpott
- Centre for Cutaneous Research, Blizard Institute, Bart's & The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom
| | | | - Francesco Di Virgilio
- Department of Morphology, Surgery and Experimental Medicine, Section of Pathology, Oncology and Experimental Biology, University of Ferrara, Ferrara, Italy
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P2X and P2Y receptors—role in the pathophysiology of the nervous system. Int J Mol Sci 2014; 15:23672-704. [PMID: 25530618 PMCID: PMC4284787 DOI: 10.3390/ijms151223672] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Revised: 12/03/2014] [Accepted: 12/06/2014] [Indexed: 12/16/2022] Open
Abstract
Purinergic signalling plays a crucial role in proper functioning of the nervous system. Mechanisms depending on extracellular nucleotides and their P2 receptors also underlie a number of nervous system dysfunctions. This review aims to present the role of purinergic signalling, with particular focus devoted to role of P2 family receptors, in epilepsy, depression, neuropathic pain, nervous system neoplasms, such as glioma and neuroblastoma, neurodegenerative diseases like Parkinson’s disease, Alzheimer’s disease and multiple sclerosis. The above-mentioned conditions are associated with changes in expression of extracellular ectonucleotidases, P2X and P2Y receptors in neurons and glial cells, as well as releasing considerable amounts of nucleotides from activated or damaged nervous tissue cells into the extracellular space, which contributes to disturbance in purinergic signalling. The numerous studies indicate a potential possibility of using synthetic agonists/antagonists of P2 receptors in treatment of selected nervous system diseases. This is of particular significance, since numerous available agents reveal a low effectiveness and often produce side effects.
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Burnstock G, Di Virgilio F. Purinergic signalling and cancer. Purinergic Signal 2014; 9:491-540. [PMID: 23797685 DOI: 10.1007/s11302-013-9372-5] [Citation(s) in RCA: 234] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2013] [Accepted: 06/06/2013] [Indexed: 01/24/2023] Open
Abstract
Receptors for extracellular nucleotides are widely expressed by mammalian cells. They mediate a large array of responses ranging from growth stimulation to apoptosis, from chemotaxis to cell differentiation and from nociception to cytokine release, as well as neurotransmission. Pharma industry is involved in the development and clinical testing of drugs selectively targeting the different P1 nucleoside and P2 nucleotide receptor subtypes. As described in detail in the present review, P2 receptors are expressed by all tumours, in some cases to a very high level. Activation or inhibition of selected P2 receptor subtypes brings about cancer cell death or growth inhibition. The field has been largely neglected by current research in oncology, yet the evidence presented in this review, most of which is based on in vitro studies, although with a limited amount from in vivo experiments and human studies, warrants further efforts to explore the therapeutic potential of purinoceptor targeting in cancer.
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Spatio-temporal spread of neuronal death after focal photolysis of caged glutamate in neuron/astrocyte co-cultures. Neurochem Int 2013; 62:1020-7. [PMID: 23538265 DOI: 10.1016/j.neuint.2013.03.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Revised: 03/13/2013] [Accepted: 03/15/2013] [Indexed: 11/22/2022]
Abstract
Glutamate-mediated excitotoxicity is now accepted as a major mechanism of ischemic neuronal damage. In the infarct core region, massive neuronal death is observed, but neurons in the surroundings of the core (ischemic penumbra) seem viable at the time of stroke. Several hours or days after a stroke, however, many neurons in the penumbra will undergo delayed neuronal death (DND). The mechanisms responsible for such DND are not fully understood. In this study, we investigated whether and how glutamate-mediated localized excitotoxic neuronal death affects surrounding neurons and astrocytes. To induce spatially-restricted excitotoxic neuronal death, a caged glutamate was focally photolyzed by a UV flash in neuron/astrocyte co-cultures. Uncaging of the glutamate resulted in acute neuronal death in the flashed area. After that, DND was observed in the surroundings of the flashed area late after the uncaging. In contrast, DND was not observed in neuron-enriched cultures, suggesting that functional changes in astrocytes, not neurons, after focal acute neuronal death were involved in the induction of DND. The present in vitro study showed that the spatially-restricted excitotoxic neuronal death resulted in DND in the surroundings of the flashed area, and suggested that the nitric oxide (NO)-induced reduction in the expression of astrocytic GLT-1 was responsible for the occurrence of the DND.
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Cosentino S, Banfi C, Burbiel JC, Luo H, Tremoli E, Abbracchio MP. Cardiomyocyte death induced by ischaemic/hypoxic stress is differentially affected by distinct purinergic P2 receptors. J Cell Mol Med 2012; 16:1074-84. [PMID: 21762374 PMCID: PMC4365886 DOI: 10.1111/j.1582-4934.2011.01382.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Blood levels of extracellular nucleotides (e.g. ATP) are greatly increased during heart ischaemia, but, despite the presence of their specific receptors on cardiomyocytes (both P2X and P2Y subtypes), their effects on the subsequent myocardial damage are still unknown. In this study, we aimed at investigating the role of ATP and specific P2 receptors in the appearance of cell injury in a cardiac model of ischaemic/hypoxic stress. Cells were maintained in a modular incubator chamber in a controlled humidified atmosphere of 95% N2 for 16 hrs in a glucose-free medium. In this condition, we detected an early increase in the release of ATP in the culture medium, which was followed by a massive increase in the release of cytoplasmic histone-associated-DNA-fragments, a marker of apoptosis. Addition of either apyrase, which degrades extracellular ATP, or various inhibitors of ATP release via connexin hemichannels fully abolished ischaemic/hypoxic stress-associated apoptosis. To dissect the role of specific P2 receptor subtypes, we used a combined approach: (i) non-selective and, when available, subtype-selective P2 antagonists, were added to cardiomyocytes before ischaemic/hypoxic stress; (ii) selected P2 receptors genes were silenced via specific small interfering RNAs. Both approaches indicated that the P2Y2 and P2χ7 receptor subtypes are directly involved in the induction of cell death during ischaemic/hypoxic stress, whereas the P2Y4 receptor has a protective effect. Overall, these findings indicate a role for ATP and its receptors in modulating cardiomyocyte damage during ischaemic/hypoxic stress.
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Rodríguez-Sinovas A, Sánchez JA, Fernandez-Sanz C, Ruiz-Meana M, Garcia-Dorado D. Connexin and pannexin as modulators of myocardial injury. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1962-70. [PMID: 21839721 DOI: 10.1016/j.bbamem.2011.07.041] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Revised: 07/20/2011] [Accepted: 07/28/2011] [Indexed: 01/02/2023]
Abstract
Multicellular organisms have developed a variety of mechanisms that allow communication between their cells. Whereas some of these systems, as neurotransmission or hormones, make possible communication between remote areas, direct cell-to-cell communication through specific membrane channels keep in contact neighboring cells. Direct communication between the cytoplasm of adjacent cells is achieved in vertebrates by membrane channels formed by connexins. However, in addition to allowing exchange of ions and small metabolites between the cytoplasms of adjacent cells, connexin channels also communicate the cytosol with the extracellular space, thus enabling a completely different communication system, involving activation of extracellular receptors. Recently, the demonstration of connexin at the inner mitochondrial membrane of cardiomyocytes, probably forming hemichannels, has enlarged the list of actions of connexins. Some of these mechanisms are also shared by a different family of proteins, termed pannexins. Importantly, these systems allow not only communication between healthy cells, but also play an important role during different types of injury. The aim of this review is to discuss the role played by both connexin hemichannels and pannexin channels in cell communication and injury. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.
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Harada K, Hide I, Seki T, Tanaka S, Nakata Y, Sakai N. Extracellular ATP differentially modulates Toll-like receptor 4-mediated cell survival and death of microglia. J Neurochem 2011; 116:1138-47. [PMID: 21210814 DOI: 10.1111/j.1471-4159.2011.07170.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The survival and death rates of inflammatory cells directly control their number and are substantially associated with the degree of inflammation. Microglia, key players in neuroinflammation, often cause excessive reactions implicated in neurological diseases. However, the mechanisms that determine microglial fate under pathological conditions remain to be elucidated. Here, we report that activation by lipopolysaccharide (LPS, a Toll-like receptor 4 ligand), an inflammation inducer, primarily promotes survival of microglia, but as its concentration is increased it induces cell death, resulting in decreased cell number. Moreover, extracellular ATP, which is released upon tissue damage, further enhanced the survival induced by a low LPS concentration and the death induced by a high LPS concentration. The survival-promoting effect of ATP was mimicked by non-hydrolyzable ATP analog, adenosine 5'-O-(3-thiotriphosphate), and also by the P2X(7) receptor agonist, 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate, and was suppressed by the P2X(7) antagonists, Brilliant Blue G and A 438079. On the contrary, the death of LPS-activated microglia was not affected by adenosine 5'-O-(3-thiotriphosphate), but enhanced by adenosine, ATP breakdown product. Thus, extracellular ATP modulates microglial survival and death in different ways involving P2X(7) receptor activation and ATP degradation to adenosine, respectively. Such Toll-like receptor 4/purinergic signaling may provide a fine regulatory system of neuroinflammation through modulating the microglial cell number.
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Affiliation(s)
- Kana Harada
- Department of Molecular and Pharmacological Neuroscience, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan
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Iwabuchi S, Kawahara K. Functional significance of the negative-feedback regulation of ATP release via pannexin-1 hemichannels under ischemic stress in astrocytes. Neurochem Int 2010; 58:376-84. [PMID: 21185900 DOI: 10.1016/j.neuint.2010.12.013] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2010] [Revised: 12/11/2010] [Accepted: 12/17/2010] [Indexed: 10/18/2022]
Abstract
The opening of pannexin-1 (Px1) hemichannels is regulated by the activity of P2X(7) receptors (P2X(7)Rs). At present, however, little is known about how extracellular ATP-sensitive P2X(7)Rs regulates the opening and closure of Px1 hemichannels. Several lines of evidence suggest that P2X(7)Rs are activated under pathological conditions such as ischemia, resulting in the opening of Px1 hemichannels responsible for the massive influx of Ca(2+) from the extracellular space and the release of ATP from the cytoplasm, leading to cell death. Here we show in cultured astrocytes that the suppression of the activity of P2X(7)Rs during simulated ischemia (oxygen/glucose deprivation, OGD) resulted in the opening of Px1 hemichannels, leading to the enhanced release of ATP. In addition, the suppression of the activity of P2X(7)Rs during OGD resulted in a significant increase in astrocytic damage. Both the P2X(7)Rs suppression-induced enhancement of the release of ATP and cell damage were reversed by co-treatment with blockers of Px1 hemichannels, suggesting that suppression of the activity of PX(7)Rs resulted in the opening of Px1 hemichannels. All these findings suggested the existence of a negative-feedback loop regulating the release of ATP via Px1 hemichannels; ATP-induced suppression of ATP release. The present study indicates that ATP, released through Px1 hemichannels, activates P2X(7)Rs, resulting in the closure of Px1 hemichannels during ischemia. This negative-feedback mechanism, suppressing the loss of cellular ATP and Ca(2+) influx, might contribute to the survival of astrocytes under ischemic stress.
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Affiliation(s)
- Sadahiro Iwabuchi
- Laboratory of Cellular Cybernetics, Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan
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Abstract
Evidence is accumulating that some forms of cell death, like apoptosis, are not only governed by the complex interplay between extracellular and intracellular signals but are also strongly influenced by intercellular communicative networks. The latter is provided by arrays of channels consisting of connexin proteins, with gap junctions directly connecting the cytoplasm of neighboring cells and hemichannels positioned as pores that link the cytoplasm to the extracellular environment. The role of gap junctions in cell death communication has received considerable interest and recently hemichannels have joined in as potentially toxic pores adding their part to the cell death process. However, despite a large body of existing evidence, especially for gap junctions, the exact contribution of the connexin channel family still remains controversial, as both gap junctions and hemichannels may furnish cell death as well as cell survival signals. An additional layer of complexity is formed by the fact that connexin proteins as such, beyond their channel function, may influence the cell death process. We here review the current knowledge on connexins and their channels in cell death and specifically address the molecular mechanisms that underlie connexin-related signaling. We also briefly focus on pannexins, a novel set of connexin-like proteins that have been implicated in cellular responses to pathological insults.
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Hopfe M, Henrich B. OppA, the ecto-ATPase of Mycoplasma hominis induces ATP release and cell death in HeLa cells. BMC Microbiol 2008; 8:55. [PMID: 18394151 PMCID: PMC2323007 DOI: 10.1186/1471-2180-8-55] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Accepted: 04/04/2008] [Indexed: 12/21/2022] Open
Abstract
Background In the facultative human pathogen Mycoplasma hominis, which belongs to the cell wall-less Mollicutes, the surface-localised substrate-binding domain OppA of the oligopeptide permease was characterised as the main ecto-ATPase. Results With the idea that extra-cellular ATP could only be provided by the infected host cells we analysed the ATP release of HeLa cells after incubation with different preparations of Mycoplasma hominis: intact bacterial cells, the membrane fraction with or without OppA, recombinant OppA as well as an ATPase-deficient OppA mutant. Release of ATP into the supernatant of the HeLa cells was primarily determined in all samples lacking ecto-ATPase activity of OppA. In the presence of the ATPase inhibitor DIDS the amount of ATP in the OppA-containing samples increased. This increase was maximal after incubation with fractions containing OppA protein indicating that OppA is involved in ATP release and subsequent hydrolysis. Real-time PCR analyses revealed that the proliferation of HeLa cells is reduced after infection with M. hominis and flow cytometry experiments established that OppA induces greater apoptosis than necrosis of HeLa cells whereas the preservation of ecto-ATPase activity of OppA induces apoptosis. Conclusion The OppA induced ATP-release and -hydrolysis induced cell death of M. hominis infected HeLa cells was predominantly due to apoptosis rather than necrosis. Future work will elucidate whether the induction of apoptosis is indispensable for survival of these non-invasive pathogen.
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Affiliation(s)
- Miriam Hopfe
- Institute of Medical Microbiology and Center for Biological Medical Research, Heinrich-Heine-University, Moorenstrasse 5, 40225 Duesseldorf, Germany.
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Vázquez-Cuevas FG, Juárez B, Garay E, Arellano RO. ATP-induced apoptotic cell death in porcine ovarian theca cells through P2X7 receptor activation. Mol Reprod Dev 2007; 73:745-55. [PMID: 16541451 DOI: 10.1002/mrd.20447] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Folliculogenesis modulation via distinct neurotransmitters is a well-documented phenomenon. Intraovarian purinergic signaling mechanisms have been identified previously in different species. However, the molecular elements involved and the physiological role of this purinergic signaling remain to be elucidated. Here, studies using RT-PCR amplification, immunoblotting, and immunofluorescence microscopy showed that murine and porcine ovaries express the P2X7 subtype receptor, a cationic receptor-channel operated by ATP. Using immunofluorescence it was demonstrated that P2X7 protein expression, in both mouse and pig, occurs specifically in the theca cells from antral follicles. Isolated porcine theca cells maintained in primary cultures and tested with 1 mM ATP or 250 microM Bz-ATP, a specific agonist of P2X7, responded with an increase in intracellular calcium concentration, as demonstrated in cells loaded with fluo-4 as calcium indicator. This strongly suggested that P2X7 receptors in theca cells are functional. Moreover, application for 24 hr of 1 mM ATP or 250 microM Bz-ATP induced apoptotic cell death as indicated by the DNA fragmentation pattern, positive TUNEL test, and annexin V binding. This ATP effect was antagonized by 300 microM PPADS and 200 microM oxidized ATP. Also, addition of 5 mM EGTA in the external medium to chelate free Ca++ decreased death cell to 24% of that produced by 200 microM Bz-ATP, suggesting that Ca++ influx participates in the phenomenon. The highly specific and functional expression of P2X7 receptors in theca cells suggest a role for ATP in modulating follicular physiology.
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Affiliation(s)
- Francisco G Vázquez-Cuevas
- Laboratorio de Neurofisiología Celular, Departamento de Neurobiología Celular y Molecular, Instituto de Neurobiología UNAM, Apdo. Postal 1-1141, Querétaro, México
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Rayment SJ, Ralevic V, Barrett DA, Cordell R, Alexander SPH. A novel mechanism of vasoregulation: ADP-induced relaxation of the porcine isolated coronary artery is mediated via adenosine release. FASEB J 2006; 21:577-85. [PMID: 17167068 DOI: 10.1096/fj.06-7050com] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
In this study, we have investigated the mechanism of ADP-induced relaxation of porcine coronary artery (PCA) rings. The P2Y receptor agonists ADP and ADPbetaS produced concentration-dependent relaxation of endothelium-denuded PCA smooth muscle with pD2 values of 5.3 and 4.9, respectively. RT-polymerase chain reaction (RT-PCR) and immunoblotting demonstrated mRNA and protein expression of P2Y1 and A2A adenosine receptors in the PCA. The nonselective P2 antagonist PPADS or the P2Y1-selective antagonist MRS2179 failed to alter ADP- or ADPbetaS-induced relaxations. Relaxations to ADP were, however, blocked by the A2A adenosine receptor-selective antagonists ZM241385 and SCH58261 (apparent pK(B) values of 9.2 and 8.9, respectively). We excluded roles for direct occupancy of A2A adenosine receptors by ADP or ADPbetaS as well as metabolism to adenosine as mechanisms for ADP-evoked relaxations. However, ADP responses were significantly enhanced in the presence of the ENT1 nucleoside transporter inhibitors dipyridamole and NBTI and were significantly inhibited by adenosine deaminase, indicating a role for extracellular adenosine. Suprafusion of [3H]-adenine-labeled PCA segments showed that ADP induced the release of a number of purines, including adenosine. These data suggest that ADP mediates relaxation of the PCA via a novel mechanism that involves adenine nucleotide-evoked adenosine release and the subsequent activation of A2A receptors.
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Affiliation(s)
- Sarah J Rayment
- School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham NG7 2UH, UK
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Wang MX, Ren LM. Growth inhibitory effect and apoptosis induced by extracellular ATP and adenosine on human gastric carcinoma cells: involvement of intracellular uptake of adenosine. Acta Pharmacol Sin 2006; 27:1085-92. [PMID: 16867263 DOI: 10.1111/j.1745-7254.2006.00342.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
AIM To study the growth inhibitory and apoptotic effects of adenosine triphosphate (ATP) and adenosine (ADO) on human gastric carcinoma (HGC)-27 cells in vitro and the mechanisms related to the actions of ATP and ADO. METHODS MTT assay was used to determine the reduction of cell viability. The morphological changes of HGC-27 cells induced by ATP or ADO were observed under fluorescence light microscope by acridine orange/ethidium bromide double-stained cells. The internucleosomal fragmentation of genomic DNA was detected by agarose gel electrophoresis. The apoptotic rate and cell-cycle analysis after treatment with ATP or ADO was determined by flow cytometry. RESULTS ATP, ADO and the intermediate metabolites, ADP and AMP, and the agonist of purinergic receptors, reduced cell viability of HGC-27 cells at doses of 0.3 and 1.0 mmol/L. The distribution of cell cycle phase and proliferation index (PI) value of HGC-27 cells changed when exposed to ATP or ADO at the concentrations of 0.1, 0.3 and 1 mmol/L for 48 h. ATP and ADO both altered the distribution of cell cycle phase via G0/G1- phase arrest and significantly decreased PI value. Under light microscope, the tumor cells exposed to 0.3 mmol/L ATP or ADO displayed morphological changes of apoptosis; a ladder-like pattern of DNA fragmentation obtained from HGC-27 cells treated with 0.1-1 mmol/L ATP or ADO appeared in agarose gel electrophoresis; ATP and ADO induced the apoptosis of HGC-27 cells in a dose-dependent manner at concentrations between 0.03-1 mmol/L. The maximum apoptotic rate of HGC-27 cells exposed to ATP or ADO for 48 h was 13.53% or 15.9%, respectively. HGC-27 cell death induced by ATP or ADO was significantly inhibited by dipyridamole (10 mmol/L), an inhibitor of adenosine transporter, but was not affected by aminophylline, a broad inhibitor of P1 receptors and pyridoxal-phosphate-6-azophenyl-2, 4-disulphonic acid tetrasodium salt (30 micromol/L), a non-selective antagonist of P2 receptors. CONCLUSION Extracellular ATP and ADO reduced the cell viability, arrested cell cycle and induced apoptosis in HGC-27 cell line by intracellular uptake of ADO. One of the main routes of ATP-induced apoptosis in HGC-27 cells is through the breakdown to adenosine.
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Affiliation(s)
- Ming-Xia Wang
- The Fourth Affiliated Hospital, Hebei Medical University, Shijiazhuang 050011, China
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Kennedy EJ, Pillus L, Ghosh G. Pho5p and newly identified nucleotide pyrophosphatases/ phosphodiesterases regulate extracellular nucleotide phosphate metabolism in Saccharomyces cerevisiae. EUKARYOTIC CELL 2006; 4:1892-901. [PMID: 16278456 PMCID: PMC1287867 DOI: 10.1128/ec.4.11.1892-1901.2005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Extracellular nucleotides play many biological roles, including intercellular communication and modulation of nucleotide receptor signaling, and are dependent on the phosphorylation state of the nucleotide. Regulation of nucleotide phosphorylation is necessary, and a specialized class of enzymes, nucleotide pyrophosphatases/phosphodiesterases (E-NPPs), has been identified in mammals to perform this function. Although the E-NPP class is conserved among complex eukaryotes, this system has not yet been identified in Saccharomyces cerevisiae. Using genetic and biochemical experiments, we show that two orthologs of the E-NPP family, referred to as Npp1p and Npp2p, exist in budding yeast and can perform nucleotide phosphate hydrolysis. This activity is enhanced during phosphate starvation, where hydrolyzed phosphates can be imported from extracellular sources and utilized to overcome phosphate starvation through the activity of the Pho5p acid phosphatase. The added compensatory effect by Pho5p is also a newly established role for Pho5p. This study demonstrates that extracellular nucleotide phosphate metabolism appears to be controlled by at least two independent regulatory mechanisms, uniting phosphate starvation with extracellular nucleotide regulation.
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Affiliation(s)
- Eileen J Kennedy
- Department of Chemistry and Biochemistry, and UCSD Cancer Center, University of California, San Diego, La Jolla, CA 92093-0347, USA
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Seetulsingh-Goorah SP. Mechanisms of adenosine-induced cytotoxicity and their clinical and physiological implications. Biofactors 2006; 27:213-30. [PMID: 17012777 DOI: 10.1002/biof.5520270119] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Extracellular ATP (ATPo) and adenosine are cytotoxic to several cancer cell lines, suggesting their potential use for anticancer therapy. Adenosine causes cytotoxicity, either when added exogenously or when generated from ATPo hydrolysis, via mechanisms which are not mutually exclusive and which involve, adenosine receptor activation, pyrimidine starvation and/or increases in intracellular S-adenosylhomocysteine: S-adenosylmethionine ratio. Given that adenosine also appears to protect against cytotoxicity via mechanisms including immunity against damage by oxygen free radicals, an understanding of the contribution of adenosine to ATPo-induced cytotoxicity is thus crucial, when considering any potential therapeutic use for these compounds. However, such an understanding has been largely hindered by the fact that many studies have not focused enough on the possibility that both ATPo and adenosine may mediate cytotoxicity in the same system. Such studies can benefit from use a range of ATPo concentrations when assessing the contribution of adenosine to ATPo-induced cytotoxicity. Whilst future molecular and pharmacological studies are needed to establish the nature of the cytotoxic adenosine receptor, it is possible that more than just one adenosine receptor type is involved and that the cytotoxic receptor(s) type is more likely to have a low affinity for adenosine. Activation of the adenosine receptor(s) would thus lead to cytotoxicity only at relatively high adenosine concentrations, while lower adenosine concentrations mediate non-cytotoxic physiological effects.
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Wang MX, Ren LM, Shan BE. Inhibitory effects of extracellular adenosine triphosphate on growth of esophageal carcinoma cells. World J Gastroenterol 2005; 11:5915-9. [PMID: 16273599 PMCID: PMC4436710 DOI: 10.3748/wjg.v11.i38.5915] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To study the growth inhibitory effects of ATP on TE-13 human squamous esophageal carcinoma cells in vitro.
METHODS: MTT assay was used to determine the inhibition of proliferation of ATP or adenosine (ADO) on TE-13 cell line. The morphological changes of TE-13 cells induced by ATP or ADO were observed under fluorescence light microscope by acridine orange (AO)/ethidium bromide (EB) double stained cells. The internucleosomal fragmentation of genomic DNA was detected by agarose gel electrophoresis. The apoptotic rate and cell cycle after treatment with ATP or ADO were determined by flow cytometry.
RESULTS: ATP and ADO produced inhibitory effects on TE-13 cells at the concentration between 0.01 and 1.0 mmol/L. The IC50 of TE-13 cells exposed to ATP or ADO for 48 and 72 h was 0.71 or 1.05, and 0.21 or 0.19 mmol/L, respectively. The distribution of cell cycle phase and proliferation index (PI) value of TE-13 cells changed, when being exposed to ATP or ADO at the concentrations of 0.01, 0.1, and 1 mmol/L for 48 h. ATP and ADO inhibited the cell proliferation by changing the distribution of cell cycle phase via either G0/G1 phase (ATP or ADO, 1 mmol/L) or S phase (ATP, 0.1 mmol/L) arrest. Under light microscope, the tumor cells exposed to 0.3 mmol/L ATP or ADO displayed morphological changes of apoptosis. A ladder-like pattern of DNA fragmentation was obtained from TE-13 cells treated with 0.1-1 mmol/L ATP or ADO in agarose gel electrophoresis. ATP and ADO induced apoptosis of TE-13 cells in a dose-dependent manner at the concentration between 0.03 and 1 mmol/L. The maximum apoptotic rate of TE-13 cells exposed to ATP or ADO for 48 h was 16.63% or 16.9%, respectively.
CONCLUSION: ATP and ADO inhibit cell proliferation, arrest cell cycle, and induce apoptosis of TE-13 cell line.
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Affiliation(s)
- Ming-Xia Wang
- School of Pharmacy, Hebei Medical University, Shijiazhuang 050017, Hebei Province, China
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18
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Sun W, Khoo HE, Tan CH. Adenosine induced apoptosis in BHK cells via P1 receptors and equilibrative nucleoside transporters. BMB Rep 2005; 38:314-9. [PMID: 15943907 DOI: 10.5483/bmbrep.2005.38.3.314] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Adenosine, as a ubiquitous metabolite, mediates many physiological functions via activation of plasma membrane receptors. Mechanisms of most of its physiological roles have been studied extensively, but research on adenosine-induced apoptosis (AIA) has only started recently. In this study we demonstrate that adenosine dose-dependently triggered apoptosis of cultured baby hamster kidney (BHK) cells. Adenosine-induced apoptotic cell death was characterized by DNA laddering, changes in nuclear chromatin morphology and phosphatidylserine staining. Apoptosis was also quantified by flow cytometry. Results suggest the involvement of adenosine A1 and A3 receptors as well as equilibrative nucleoside transporters in apoptosis induced by adenosine. These results indicate a receptor-transporter co-signaling mechanism in AIA in BHK cells. The involvement of A1 and A3 receptors also implies a possible apoptotic pathway mediated by G protein-coupled receptors.
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Affiliation(s)
- Wentian Sun
- Department of Biochemistry, Faculty of Medicine, National University of Singapore, 10 Kent Ridge Crescent, Singapore, 119260, Republic of Singapore
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19
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Krysko DV, Leybaert L, Vandenabeele P, D'Herde K. Gap junctions and the propagation of cell survival and cell death signals. Apoptosis 2005; 10:459-69. [PMID: 15909108 DOI: 10.1007/s10495-005-1875-2] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Gap junctions are a unique type of intercellular channels that connect the cytoplasm of adjoining cells. Each gap junction channel is comprised of two hemichannels or connexons and each connexon is formed by the aggregation of six protein subunits known as connexins. Gap junction channels allow the intercellular passage of small (< 1.5 kDa) molecules and regulate essential processes during development and differentiation. However, their role in cell survival and cell death is poorly understood. We review experimental data that support the hypothesis that gap junction channels may propagate cell death and survival modulating signals. In addition, we explore the hypothesis that hemichannels (or unapposed connexons) might be used as a paracrine conduit to spread factors that modulate the fate of the surrounding cells. Finally, direct signal transduction activity of connexins in cell death and survival pathways is addressed.
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Affiliation(s)
- D V Krysko
- Department of Human Anatomy, Embryology, Histology and Medical Physics, Ghent University, 9000 Ghent, Belgium.
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20
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Cavaliere F, Nestola V, Amadio S, D'Ambrosi N, Angelini DF, Sancesario G, Bernardi G, Volonté C. The metabotropic P2Y4 receptor participates in the commitment to differentiation and cell death of human neuroblastoma SH-SY5Y cells. Neurobiol Dis 2005; 18:100-9. [PMID: 15649700 DOI: 10.1016/j.nbd.2004.09.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2004] [Revised: 08/31/2004] [Accepted: 09/07/2004] [Indexed: 01/19/2023] Open
Abstract
Extracellular nucleotides exert a variety of biological actions through different subtypes of P2 receptors. Here we characterized in the human neuroblastoma SH-SY5Y cells the simultaneous presence of various P2 receptors, belonging to the P2X ionotropic and P2Y metabotropic families. Western blot analysis detected the P2X1,2,4,5,6,7 and P2Y1,2,4,6, but not the P2X3 and P2Y12 receptors. We then investigated which biological effects were mediated by the P2Y4 subtype and its physiological pyrimidine agonist UTP. We found that neuronal differentiation of the SH-SY5Y cells with dibutiryl-cAMP increased the expression of the P2Y4 protein and that UTP itself was able to positively interfere with neuritogenesis. Moreover, transient transfection and activation of P2Y4 also facilitated neuritogenesis in SH-SY5Y cells, as detected by morphological phase contrast analysis and confocal examination of neurofilament proteins NFL. This was concurrent with increased transcription of immediate-early genes linked to differentiation such as cdk-5 and NeuroD6, and activity of AP-1 transcription family members such as c-fos, fos-B, and jun-D. Nevertheless, a prolonged activation of the P2Y4 receptor by UTP also induced cell death, both in naive, differentiated, and P2Y4-transfected SH-SY5Y cells, as measured by direct count of intact nuclei and cytofluorimetric analysis of damaged DNA. Taken together, our data indicate that the high expression and activation of the P2Y4 receptor participates in the neuronal differentiation and commitment to death of SH-SY5Y cells.
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21
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Velthuis JHL, Gavric Z, de Bont HJGM, Nagelkerke JF. Impaired activation of caspases and prevention of mitochondrial dysfunction in the metastatic colon carcinoma CC531s-m2 cell line. Biochem Pharmacol 2004; 69:463-71. [PMID: 15652237 DOI: 10.1016/j.bcp.2004.10.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2004] [Accepted: 10/27/2004] [Indexed: 11/28/2022]
Abstract
In a previous paper we described the properties of a rapidly metastasizing cell line CC531s-m2 derived from the poorly metastasizing CC531s cell. The m2-cell line was relatively resistant to killing by NK cells. Both CD95L and TRAIL mediated apoptosis was decreased in the m2-cell line. Now, by flow cytometrical analysis of intra- and extra-cellular expressed receptors, we show that the localization of the receptors for CD95L and TRAIL was not altered in the CC531s-m2 cells as compared to the parental cell line. Subsequently caspase-activation and mitochondrial function were studied by enzymatic cleavage of fluorescent caspase-substrates and retention of the mitochondrial dye rhodamine-123, respectively. The activation of caspases as well as the loss of the mitochondrial membrane potential (MMP) was less in the CC531s-m2 cell line upon CD95L- and TRAIL-signalling. Furthermore, the sensitivity of the CC531-m2 towards cisplatin-induced apoptosis was strongly decreased. This was consistent with less mitochondrial damage, delayed caspase cleavage and decreased caspase activity. Altogether, we conclude that an Natural Killer-cell insensitive cell is less sensitive to CD95L- and TRAIL-induced apoptosis as well as anti-cancer drug induced apoptosis by prevention of mitochondrial damage and activation of caspases.
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Affiliation(s)
- Jurjen H L Velthuis
- Division of Toxicology, Leiden/Amsterdam Center for Drug Research, Leiden University, Gorlaeus Laboratrory, P.O. Box 9502, 2300 RA Leiden, The Netherlands
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22
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D'Ambrosi N, Costanzi S, Angelini DF, Volpini R, Sancesario G, Cristalli G, Volonté C. 2-ClATP exerts anti-tumoural actions not mediated by P2 receptors in neuronal and glial cell lines. Biochem Pharmacol 2004; 67:621-30. [PMID: 14757162 DOI: 10.1016/j.bcp.2003.09.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We investigated the effects of the ATP analogue and P2 receptor agonist 2-ClATP on growth and survival of different neuronal (PC12, PC12nnr5 and SH-SY5Y) and glial (U87 and U373) cell lines, by the use of direct count of intact nuclei, fluorescence microscopy, fluorescence-activated cell sorter analysis (FACS) and high pressure liquid chromatography (HPLC). 2-ClATP lowered the number of cultured PC12nnr5, SH-SY5Y, U87 and U373 cells to almost 5%, and of PC12 cells to about 35% after 3-4 days of treatment. EC(50) was in the 5-25 microM range, with 2-ClATP behaving as a cytotoxic or cytostatic agent. Analysis of the biological mechanisms demonstrated that pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (P2 receptor antagonist and nucleotidases inhibitor), but not Caffeine or CGS-15493 (P1 receptor antagonists) effectively prevented 2-ClATP-induced toxicity. 2-ClATP metabolic products (2-ClADP, 2-ClAMP, 2-Cladenosine) and new synthesis derivatives (2-CldAMP, 2-Cldadenosine-3',5'-bisphosphate and 2-CldATP) exerted similar cytotoxic actions. Inhibition of both serum nucleotidases and purine nucleoside transporters strongly reduced 2-ClATP-induced cell death, which was conversely increased by the nucleotide hydrolyzing enzyme apyrase. The adenosine kinase inhibitor 5-iodotubericidin totally prevented 2-ClATP or 2-Cladenosine-induced toxicity. In summary, our findings indicate that 2-ClATP exerts either cell cycle arrest or cell death, acting neither on P2 nor on P1 receptors, but being extracellularly metabolized into 2-Cladenosine, intracellularly transported and re-phosphorylated.
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Affiliation(s)
- Nadia D'Ambrosi
- Fondazione Santa Lucia, Cellular Neurobiology Unit, Rome, Italy
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23
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Burnstock G, Knight GE. Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 240:31-304. [PMID: 15548415 DOI: 10.1016/s0074-7696(04)40002-3] [Citation(s) in RCA: 573] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.
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Affiliation(s)
- Geoffrey Burnstock
- Autonomic Neuroscience Institute, Royal Free and University College Medical School, London NW3 2PF, United Kingdom
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24
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Kalvelyte A, Imbrasaite A, Bukauskiene A, Verselis VK, Bukauskas FF. Connexins and apoptotic transformation. Biochem Pharmacol 2003; 66:1661-72. [PMID: 14555247 PMCID: PMC3689318 DOI: 10.1016/s0006-2952(03)00540-9] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We examined the influence of connexin (Cx) expression on the development of apoptosis in HeLa parental cells (coupling deficient cell line) and HeLa cells expressing wild-type Cx43 and Cxs fused with enhanced green fluorescent protein (EGFP). EGFP was attached to the C-terminus of Cx32 and Cx43, Cx32-EGFP and Cx43-EGFP, respectively, and to the N-terminus of Cx32, EGFP-Cx32. All fusion proteins assembled into junctional plaques (JPs) at areas of cell-cell contact, but only the C-terminal fusion proteins formed functional gap junction (GJ) channels as well as hemichannels. In each cell line, apoptosis was induced by treatment with various agents including anisomycin, camptothecin, cis-platinum, colchicine, cycloheximide, etoposide, staurosporin and taxol. Using fluorescence microscopy, time-lapse imaging and dual whole-cell voltage clamp techniques, we correlated the changes in functional properties of GJ channels and Cx distribution with the progression of apoptosis based on cells' labeling with acridine orange and ethidium bromide (EB). The early phase of apoptosis (a viable apoptotic (VA) state) was characterized by shrinkage of the cells and by increased internalization of JPs accompanied by decreased cell-cell coupling. The apoptotic reagents had no direct effect on electrical cell-cell coupling. Transformation from a VA to a nonviable apoptotic (NVA) state was faster in HeLa cells expressing Cx43 or Cx43-EGFP than in HeLa parental cells. The potent GJ uncoupler, octanol, slowed the transition of HelaCx43-EGFP cells into a NVA state. In the absence of apoptotic reagents, the rate of EB uptake was higher in HeLaCx43-EGFP than in HeLa parental cells consistent with the presence of open Cx43-EGFP hemichannels. However, in both cell lines the rate of EB uptake decreased proportionally during the development of apoptosis suggesting that membrane permeability ascribed to Cx hemichannels is reduced. Cells expressing Cx32-EGFP and EGFP-Cx32 demonstrate the same apoptotic patterns as HeLaCx43-EGFP and HeLa parental cells, respectively. Intracellular levels of ATP in HeLaCx43-EGFP cells were substantially lower than in HeLa parental cells, and ATP added to the medium abolished the accelerated transition from a VA to a NVA state in HeLaCx43-EGFP cells. In summary, Cx32 or Cx43 accelerates transformation of cells into a NVA state or secondary necrosis and this depends on the ability of Cxs to form functional GJ channels and hemichannels.
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Affiliation(s)
- Audrone Kalvelyte
- Laboratory of Developmental Biology, Institute of Biochemistry, 12
Mokslininku Str., LT-2600 Vilnius, Lithuania
| | - Ausra Imbrasaite
- Laboratory of Developmental Biology, Institute of Biochemistry, 12
Mokslininku Str., LT-2600 Vilnius, Lithuania
| | - Angele Bukauskiene
- Department of Neuroscience, Albert Einstein College of Medicine, 1300
Morris Park Avenue, New York, NY 10461, USA
| | - Vytas K. Verselis
- Department of Neuroscience, Albert Einstein College of Medicine, 1300
Morris Park Avenue, New York, NY 10461, USA
| | - Feliksas F. Bukauskas
- Department of Neuroscience, Albert Einstein College of Medicine, 1300
Morris Park Avenue, New York, NY 10461, USA
- Corresponding author. Tel.: +1-718-430-4130; fax:
+1-718-430-8944. (F.F. Bukauskas)
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25
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Wen LT, Knowles AF. Extracellular ATP and adenosine induce cell apoptosis of human hepatoma Li-7A cells via the A3 adenosine receptor. Br J Pharmacol 2003; 140:1009-18. [PMID: 14530217 PMCID: PMC1574113 DOI: 10.1038/sj.bjp.0705523] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
1. Extracellular ATP is a potent signaling molecule that modulates a myriad of cellular functions through the activation of P2 purinergic receptors and is cytotoxic to a variety of cells at higher concentrations. The mechanism of ATP-elicited cytotoxicity is not fully understood. In this study, we investigated the effect of extracellular ATP on the human hepatoma Li-7A cells. 2. We observed a time- and dose-dependent growth inhibition of Li-7A cells by ATP, which is accompanied by an increase in the active form of caspase-3 as well as increased cleavage of its substrate, poly (ADP-ribose) polymerase. The cytotoxic effect of extracellular ATP was not mediated by the P2X7 receptor, since (1).the effect was not abolished by the P2X7 receptor antagonists oxidized ATP and KN-62, and (2).extracellular ADP, AMP, and adenosine were also cytotoxic. 3. We found that ATP and ADP were degraded to adenosine by Li-7A cells and that treatment of Li-7A cells by adenosine resulted in growth inhibition and caspase-3 activation, indicating that adenosine is the apoptotic agent. Using adenosine receptor agonists and antagonists, as well as inhibitors of adenosine transport and deamination, we showed that the cytotoxic effect of adenosine is specifically mediated by the A3 receptor even though transcripts of A1, A2A, A2B, and a splice variant of the P2X7 receptors were detected in Li-7A cells by RT-PCR. 4. Cytotoxicity caused by exogenous ATP and adenosine was completely abolished by the caspase-3 inhibitor Z-DEVD-FMK, demonstrating the central role of caspase-3 in apoptosis of Li-7A cells.
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MESH Headings
- Adenine/analogs & derivatives
- Adenine/pharmacology
- Adenosine/metabolism
- Adenosine/pharmacology
- Adenosine Deaminase Inhibitors
- Adenosine Diphosphate/pharmacology
- Adenosine Monophosphate/pharmacology
- Adenosine Triphosphate/pharmacology
- Apoptosis/drug effects
- Apoptosis/genetics
- Biological Transport/drug effects
- Carcinoma, Hepatocellular/genetics
- Carcinoma, Hepatocellular/metabolism
- Carcinoma, Hepatocellular/pathology
- Caspase 3
- Caspases/genetics
- Caspases/metabolism
- Cell Division/drug effects
- Cell Line
- Cell Line, Tumor
- Coformycin/pharmacology
- Dipyridamole/pharmacology
- Dose-Response Relationship, Drug
- Enzyme Inhibitors/pharmacology
- Gene Expression Regulation/drug effects
- Humans
- In Situ Nick-End Labeling
- Nucleosides/metabolism
- Oligonucleotide Array Sequence Analysis
- Receptor, Adenosine A3/genetics
- Receptor, Adenosine A3/metabolism
- Receptors, Purinergic P2/genetics
- Receptors, Purinergic P2/metabolism
- Receptors, Purinergic P2X7
- Reverse Transcriptase Polymerase Chain Reaction
- Time Factors
- Uridine Triphosphate/pharmacology
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Affiliation(s)
- Long T Wen
- Department of Biology, San Diego State University, San Diego, CA 92182-1030, USA.
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26
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Goding JW, Grobben B, Slegers H. Physiological and pathophysiological functions of the ecto-nucleotide pyrophosphatase/phosphodiesterase family. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1638:1-19. [PMID: 12757929 DOI: 10.1016/s0925-4439(03)00058-9] [Citation(s) in RCA: 264] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) multigene family contains five members. NPP1-3 are type II transmembrane metalloenzymes characterized by a similar modular structure composed of a short intracellular domain, a single transmembrane domain and an extracellular domain containing a conserved catalytic site. The short intracellular domain of NPP1 has a basolateral membrane-targeting signal while NPP3 is targeted to the apical surface of polarized cells. NPP4-5 detected by database searches have a predicted type I membrane orientation but have not yet been functionally characterized. E-NPPs have been detected in almost all tissues often confined to specific substructures or cell types. In some cell types, NPP1 expression is constitutive or can be induced by TGF-beta and glucocorticoids, but the signal transduction pathways that control expression are poorly documented. NPP1-3 have a broad substrate specificity which may reflect their role in a host of physiological and biochemical processes including bone mineralization, calcification of ligaments and joint capsules, modulation of purinergic receptor signalling, nucleotide recycling, and cell motility. Abnormal NPP expression is involved in pathological mineralization, crystal depositions in joints, invasion and metastasis of cancer cells, and type 2 diabetes. In this review we summarize the present knowledge on the structure and the physiological and biochemical functions of E-NPP and their contribution to the pathogenesis of diseases.
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Affiliation(s)
- James W Goding
- Department of Pathology and Immunology, Monash Medical School, Monash University, 3181, Victoria, Prahran, Australia
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